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E. coli the enemy

It's been in the news a lot, but for those who've missed it there's a particularly deadly strain of E. coli that has reared its head in Germany. The source of the bacteria is not yet known although both cucumbers and beansprouts have been blamed, and German authorities are advising people to stay away from raw leafy vegetables. Vegetables don't usually harbour their own strains of E. coli, but the thought is that animal manure (which most definitely does contain E. coli) used to fertilise the vegetables may be carrying the deadly strain.

This plate is more deadly than you can possibly imagine

I talk about E. coli a lot in my blog as I use it for most of my experiments. The strain I use is called K12 and is completely harmless to humans. It's also used in sterile conditions and not allowed to leave the lab. The strain that's causing panic in Germany is called O104:H4 which is an enterohemorrhagic strain which can cause bloody diarrhoea and also attack the kidneys. Working from news sources (as there don't seem to be any papers out yet!) it seems to have picked up the DNA with a kidney damaging toxin as well as having proteins that help it to stick strongly to the intestinal cell wall. Other bloggers have looked at this in more exact detail (and shared their findings, which is pretty awesome), including which parts of the DNA have changed in this new strain.

The labelling isn't just arbitrary either, it tells you exactly what antigens the bacteria is carrying, and antigens are the things that the immune system recognises to help your body attack the disease. There are three different types of antigens in the E. coli species; O (in the new deadly strain), H and K (in my lab strain). The letter and number after the : mark "O104:H4" refers to the flagella antigen. Strains which share the same antigen types will have similar patterns of virulence.

As well as trying to understand the genetic code and how this strain differs from other deadly and non-deadly E. coli, scientists are also trying to find exactly where the bacteria are coming from, testing vegetable sources in an attempt to isolate it. Both cucumbers and beansprouts have now been tested for the strain isolated from patients, and both have shown negative results.

Understanding where the deadly strain arises from is less useful in terms of the scientific investigation, but crucial for stopping the disease from spreading, and helping to understand how to avoid such strains developing in the future.

If you're worried about the vegetables you're eating then the best advice I can give is to cook before eating. E. coli are not able to withstand the high temperatures of cooking and unlike bacteria such as clostridium they do not release toxins onto the food. Clostidium produce exotoxins directly onto your food whereas E. coli produce endotoxins once they get into the body. For the more sciencey minded, it's Gram positive bacteria which tend to produce exotoxins, whereas Gram negatives produce the endotoxins.

It's only once the E. coli enter your body that they start producing 'toxins' and these toxins are usually parts of the bacteria as they are broken down by the immune system. If you manage to destroy the bacteria before eating the food, then it will be pretty much safe to consume. Note that this technique does not work for exotoxins, which are actively secreted by the bacteria (Gram positives like secreting things) onto food before you eat it.

Studying bacteria does sometimes feel like a little niche set slightly apart from the real world, which is full of lumbering eukaryotes making complex non-rational interactions. News like this an interesting reminded that bacteria don't just affect health, but also have strong economic and political implications. Spanish cucumber salesmen are trying to sue Germany, Russia's getting all smug about EU health regulations, and German tourism is being affected. All because of E. coli.

4 comments:

Yes, I'm up and running now! There's a mini-series on plant defence against pathogens that I should be putting up over the weekend and start of next week, and then there'll be all the papers as I start to read up for my PhD. :)